Besides the desired effects, adverse side effects must also be taken into consideration in connection with the administration and dosing of anesthetics. For example, an anesthetic overdosage may have fatal consequences; on the other hand, underdosing, associated with traumatic perceptions on the part of the patient, are likewise undesired. It is therefore of great interest to monitor the current concentration of the active ingredients in the patient's body and to effectively control it, if necessary, in the course of the anesthesia.
Even though monitoring of the concentration in the breathing gas of the patient is state of the art in the case of volatile anesthetics, and the expiratory concentration of the anesthetic gas is used as an indicator for the assessment of the anesthetic action, no comparable functioning measuring systems are known for the nonvolatile anesthetics administered intravenously and especially propofol.
Based on the rapid redistribution and metabolism of propofol in the patient's body, this anesthetic must be redosed continuously in order to maintain a constantly effective concentration. The dosing has been hitherto performed either according to preset dosing schemes or by means of microprocessor-controlled injection pumps, which infuse the drug on the basis of pharmacokinetic data (TCI=Target Controlled Infusion); see, e.g., the journal British Journal of Anaesthesia, 90 (5), pp. 617 to 623 (2003), A. Quattara et al.: Target-controlled infusion of propofol and remifentanil in cardiac anaesthesia: influence of age on predicted effect-site concentrations. The dosing by means of “TCI” is inaccurate according to this reference, especially in older patients.
The control of anesthesia according to the state of the art is thus based only on the predictions of a model rather than on actual concentration determinations at the patient. Considerable deviations occur here between the assumed concentration and the actual concentration in the patient, and there is, e.g., an anesthetic overdosage with the associated adverse cardiovascular effects such as a drop in blood pressure.
The rapid, direct determination of the current propofol concentration in the patient, associated with the possibility of controlling the propofol concentration by varying the rate of infusion, is not possible with the complicated laboratory methods known so far, such as liquid chromatography.